The british heart foundation recommends this...
If you have shortness of breath with mild exertion, but symptoms or medication have not changed in the last 6 weeks, there is no restriction.
I agree with Kenkeith, I don't think you will notice anything.
However, an important factor not to overlook is if you are anxious about flying. If you are even a little bit nervous of flying, don't forget to mention this to your Doctor.
If your blood pressure is under control, that would not present a problem.
In general, air travel does not pose great risks to most patients with heart disease. Cardiac "incidents" occur only in 1 to 2 patients per million during air travel. However, some heart patients need to avoid flying, at least temporarily, because of the increased risk posed by being confined to a high-altitude (and therefore low-oxygen) compartment. (Airplane cabins are pressurized to the equivalent of approximately 10,000 feet above sea level.)
Patients should not fly if:
•they have had a heart attack (myocardial infarction) within the past two weeks
•they have had coronary artery stent placement within the past two weeks
•they have had coronary artery bypass surgery within the past three weeks (longer if they have had pulmonary complications)
•they have unstable angina, poorly controlled heart failure, or uncontrolled arrhythmias
Moderate mitral valve stenosis should not be any problem, however, it is usually prudent to talk to the treating doctor. With MV stenosis the left atrium has higher resistance to pump against to supply blood to the left ventricle. It is possible the restriction of blood flow due to the MV stenosis, may restrict a good supply of blood if a higher demand for blood/oxygen output....but there are oxygen masks available, and I doubt you would have a problem.
Thanks for your question. Take care.